1. Field of the Invention
The present invention relates to an electromagnetic wave detecting element. In particular, the present invention relates to an electromagnetic wave detecting element that includes plural collection electrodes that collect charges generated in a semiconductor layer by electromagnetic waves being irradiated.
2. Description of the Related Art
Radiation image detection devices such as FPDs (flat panel detectors), in which an X-ray sensitive layer is disposed on a TFT (thin film transistor) active matrix substrate and that can convert X-ray information directly into digital data, and the like, have been put into practice in recent years. As compared with a conventional imaging plate, an image can be confirmed immediately at an FPD. Further, the FPD has the advantage that video images as well can be confirmed. Therefore, the popularization of FPDs has advanced rapidly.
Various types of radiation image detection devices are proposed. For example, there is a direct-conversion-type radiation image detection device that converts radiation directly into charges and accumulates the charges. Moreover, there is an indirect-conversion-type radiation image detection device that once converts radiation into light at a scintillator of CsI:Tl, GOS (Gd2O2S:Tb), or the like, and, at semiconductor layer, converts the converted light into charges and accumulates the charges.
As an example, FIG. 8 shows a plan view illustrating the constitution of a single pixel unit of a direct-conversion-type electromagnetic wave detecting element 10′. Further, a cross-sectional view along line A-A of FIG. 8 is shown in FIG. 9.
As shown in FIG. 8, the electromagnetic wave detecting element 10′ is provided with sensor portions 103′ and TFT switches 4′, which correspond with intersection portions of plural scan lines 101′ and plural signal lines 3′, which are disposed to intersect one another.
As shown in FIG. 9, the sensor portion 103′ includes a semiconductor layer 6′, an upper electrode 7′ and a lower electrode 11′. The semiconductor layer 6′ generates charge when irradiated with X-rays. The upper electrode 7′ applies a bias voltage to the semiconductor layer 6′, and the lower electrode 11′ collects the charge generated in the semiconductor layer 6′.
For example, when X-rays are irradiated from the upper side of FIG. 9, the semiconductor layer 6′ generates charges thereinside. If a positive bias voltage is applied to the upper electrode 7′ such that the upper electrode 7′ is at a positive potential relative to the lower electrode 11′, then among the charges generated inside the semiconductor layer 6′, holes are gathered at the lower electrode 11′ and are accumulated at a charge storage capacitor 5′ which is electrically connected to the lower electrode 11′. On the other hand, if a negative bias is applied to the upper electrode 7′, then among the charges generated inside the semiconductor layer 6′, electrons are gathered at the lower electrode 11′ and are accumulated at the charge storage capacitor 5′. Charge amounts that are generated in the semiconductor layer 6′ vary in accordance with irradiated X-ray quantities. Therefore, charges corresponding to image information carried by the X-rays are accumulated in the charge storage capacitors of the respective pixels. Subsequently, signals turning the TFT switches 4′ ON are sequentially applied through the scan lines 101′ illustrated in FIG. 8. Then the charges accumulated in the charge storage capacitors 5′ are fed out through the signal lines 3′.
However, in this kind of electromagnetic wave detecting element 10′, a portion of the charges generated in the semiconductor layer 6′ are trapped in the semiconductor layer 6′. Consequently, a portion of the generated charges may not be collected by the lower electrode 11′, and a residual image may be formed.
FIG. 10 schematically illustrates a state in which the charges generated in the semiconductor layer 6′ at a region of the scan line 101′ of this kind of electromagnetic wave detecting element 10′ are being collected. Note that FIG. 10 shows a cross-sectional view along line B-B of FIG. 8A.
As shown in FIG. 10, the generated charges are collected by the lower electrodes 11′. However, a portion of the generated charges are trapped at the semiconductor layer 6′.
In Japanese patent application laid-open (JP-A) No. 2004-33659, a technology that suppresses the creation of a residual image is described. In this technology, a light generator (a backlight device) is disposed at a rear face of the electromagnetic wave detecting element 10′, and light is illuminated onto the electromagnetic wave detecting element 10′ by the light generator.
When the technology recited in JP-A No. 2004-33659 is employed and light is illuminated onto the electromagnetic wave detecting element 10′, there is a consistent effect of suppression of the creation of residual images which are caused by trapping of charges.
However, further suppression of residual images has been called for in recent years. Due thereto, suppression of the trapping of charges in the semiconductor layer 6′ is essential for this.